I doubt that many people will be buying desktops in 2020.
Instead, I'm imagining the average laptop will be something with a:
A 14" 4K resolution touch screen that is convertible to a tablet form factor
"Windows 10" - which will still suck. Sadly, most of the desktop Linux distributions will probably still suck as well.

A 4 GHz 8 core processor that will use about 10 watts of power at max speed
Lithium Ion batteries that still aren't much better than today... Seriously, it's been over a decade since we've had any real breakthroughs in battery technology that actually made it out of the lab and into production

32 GB of memory
A 3 TB hard drive or 1 TB SSD
Integrated graphics that is about twice as powerful as 2 GeForce 680's in SLI.... yet it still won't be good enough to play the latest version of Crysis.